Thursday 22 April 2010 18.00 EDT
First published on Thursday 22 April 2010 18.00 EDT

"I'll be especially nervous at the Proms," Paul Lewis tells me. I can understand why. The pianist will be playing all five Beethoven piano concertos in four concerts at the Royal Albert Hall, with different orchestras and different conductors. Even for a pianist who's played in the best halls all over the world, from Vienna to Los Angeles, who counts Alfred Brendel as his closest mentor, and who has recorded a complete cycle of classical music's "new testament" – Beethoven's 32 piano sonatas – the prospect of doing all five of the concertos is a daunting prospect. "There's no arrival with these pieces," 37-year-old Lewis says. "You never think you've created the definitive performance. It's only ever a sort of work in progress. There are some places, like the opening of the 4th [where the piano has a short solo before the orchestra play a note] where you open the score and think: 'Oh, shit!'"

But at least Lewis has had the ideal preparation to get these five cornerstones of the classical repertoire into his fingers and brain. He's just recorded them with the BBC Symphony Orchestra and their conductor, Jirˇí Beˇlohlávek, and he'll be playing the 1st and 4th concertos with the same forces during the Proms. And he's no longer scared by the opening of the 4th. "In a large concert hall like the Albert Hall, where it's so huge you almost feel like you're playing in an outdoor arena, you don't hear the incredibly delicate balance between the notes. So you just have to remember that – and avoid driving yourself round the twist thinking about it."

Liverpool-born Lewis has a reputation for being more cerebral than crazy in his performances. If you look at the covers of his Beethoven albums, you get the impression that he's a very serious young man, his intense blue eyes lost in Beethovian deep thought, a Ludwigesque tousle of curly hair the only hint of more chaotic passions. His recordings of the sonatas impress for their intellectual command, their control of pacing, and for musical architecture – their seriousness, in other words. But meeting him at his home, Lewis isn't lost in ethereal spheres of abstract contemplation. He laughs a lot, he does a wicked impression of Brendel's mannerisms, and is full of self-deprecating modesty. And if his personality weren't already rounded enough, his family keeps his feet firmly on the ground.

He's married to Bjørg Vaernes, the Norwegian cellist of the Vertavo Quartet ("I played the cello as a young boy, really badly, and that was my dream; so instead of becoming a cellist, I married one"), and they have three young children. His house in north-west London is a playground of children's toys and musical instruments. To get to his purpose-built music hut at the end of the garden, with its two Steinways, you have to negotiate footballs, slides and sandpits. And although it's soundproofed, I can still hear his youngest, Otto, pleading for his dad's attention once we're inside.

Yet for all of these trappings of familial normality, Lewis is one of the most driven musicians you could meet. He obsesses over the repertoire he plays – having immersed himself in Beethoven over the last couple of years, he moves on to Schubert for the next two seasons – and keeps to a regular practice of four to five hours a day. And when he's passionate about a subject, he talks with explosive intensity – and anger: everything from Barry Cooper's recent edition of the Beethoven Sonatas ("don't get me started – I find it very annoying") to classical music's place in society ("all this elitism stuff – it's bullshit").

His way of talking is just like his playing: all that intellectual focus and commitment is made meaningful in the moments when Lewis loses it, when he unleashes the extremities of what the piano can do. Listen to his recording of the opening of the Hammerklavier Sonata, with its unstoppable energy, or the supernatural radiance he finds in the second movement of Beethoven's last sonata, and you'll hear what I mean.

Lewis has made himself a specialist in exactly the Viennese classical repertoire that Brendel made his own: Beethoven, Mozart, Schubert. But that's not how he started out. His first love was the colouristic virtuosity of composers such as Balakirev, Busoni, Scriabin and Rachmaninov, some of the most difficult piano music ever written.

"When I was at Chetham's School of Music in Manchester, I got through that kind of repertoire with more determination than skill of any kind" – Lewis's false modesty again, since begin able to play Rachmaninov in your teens makes you a borderline musical prodigy – "and when I was 15 or 16, I was set on going to Moscow to continue my studies there." The fact that Lewis didn't continue a career as a Russian music virtuoso is thanks to the Guildhall school in London, and his ongoing relationship with Brendel, which started when he played for him in a masterclass in 1993.

But he's recently been playing Rachmaninov again. "I got the 3rd Piano Concerto out the other day, just for fun" – as you do – "and it's funny how music transports you back to a different time of life. For a split second I was back at the Guildhall, in one of the practice rooms at 7 in the morning. The music brought me right back to that time – I could smell it, taste it. I wouldn't close the door to Rachmaninov, or to any of this music. But it just doesn't seem like me these days, playing all this Beethoven and Schubert."

There's another side to Lewis that he has never publicly revealed. As a teenager, he studied composition. "I got far enough to realise that I didn't have a language, a voice of my own." He was 18 when he gave up. "It was like really bad Prokofiev. There was a lot of piano and chamber music, including a bassoon sonata – the sonata that Prokofiev or Poulenc never wrote! It was all really derivative." But then, in Lewis's music room, underneath precious facsimile opies of autograph manuscripts of Schubert sonatas and Beethoven concertos, I spy a Lewis original, one of his own handwritten pieces. "Oh, that's a scherzo I wrote when I was 15 or 16, I think. Let's have a go – it's actually impossible to play." At which point, Paul Lewis the thirtysomething pianist meets his teenage-composer self. It's a glorious encounter. He plays the scherzo almost perfectly, including all of its extravagant hand-crossing, and exuberant, overcomplicated notation. "Do you recognise that?" he asks as his hands fly over his Steinway. "There's a bit in Prokofiev's Second Piano Concerto which sounds exactly like that – and this tune? That's from his First Violin Concerto. It's so derivative," he shouts, gleefully, over his playing. Pastiche it may be, but it's also pretty astonishing for a teenage composition.

There's clearly more to Lewis than meets the eye. He recently stopped flying lessons. "I got too responsible, you know, married with kids, and thought I should take that element of risk out of my life. I went solo but didn't get my licence. But I did have a couple of lessons in microlights. Now that's really dangerous," he smiles.

But when I leave him, his thoughts are still with Beethoven, that "belligerent, outspoken, deaf German. You know, he's too bloody-minded to make what he writes convenient for the piano. When he has an idea, he just writes what he wants to, and if sometimes it almost doesn't work on the instrument – well, that's your problem. You just have to find a way through it." Like Lewis, like Ludwig: if he can master the impossibilities of his own teenage scherzo, the Beethoven concertos should be a cinch.

Paul Lewis performs the five Beethoven piano concertos at the Proms. Details: bbc.co.uk/proms.